Field of the Invention
The invention relates to a method of applying a layer of lacquer to an upper side of a printed medium, as well as to a corresponding apparatus.
In particular, in digital photography, the digital photographs must be printed. The result of such printing does not always look particularly attractive. The paper used for printing has a dull rather than shiny finish. It is especially disadvantageous in preparing a prospectus or similar document if a shiny print cannot be produced directly or suitable printing paper is not available or, for example, if a printer is used that cannot generate such prints.
Thus there are a number of situations associate with the preparation of printed documents in which it is desirable to cover the material with a glossy layer after it has been printed, for instance with a thin layer of lacquer, so that the print will have a more pleasant, attractive appearance.
The so-called lamination technique has conventionally been used for this purpose. A piece of cellophane or PVC film to which a layer of adhesive has been applied is placed on the printed upper side of a printed medium, so as to obtain a glossy surface. This method cannot readily be implemented inside a printing machine. The adhesive-coated PVC or cellophane film is pulled off a roll and cut to shape, so that it can then be placed on the printed side of the printed medium, in particular rolled onto the surface. It is important here to avoid air inclusions. For the procedural steps just described, separate devices are needed to store the film, retrieve it from storage and put it into position. The mechanical technology required is extremely elaborate.
As an alternative, in the so-called xe2x80x9cwet-in-wetxe2x80x9d method, dispersion lacquer is applied to the upper side of a printed medium while it is still wet, i.e. has just been printed. This is followed by drying, as the medium is transported over a relatively long distance, 4 to 8 m, under IR irradiation. In this method, it very often happens that the lacquered surface becomes dull, as a result of etching of the lacquer layer from the color side. Furthermore, in this method, very elaborate mechanical technology is again needed. In particular, because the drying segment of the process requires transport over such a long distance, the machinery can be installed only in correspondingly large buildings or factory halls.
It is accordingly an object of the invention to provide a method and an apparatus for applying a layer of lacquer to an upper side of a printed medium that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that apply a layer of lacquer to the upper side of a printed medium to ensure a glossy finish of high quality with an extremely short processing distance, and can employ the wet-in-wet procedure, so as also to enable a so-called faxc3xa7on lacquering without problems.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of applying a lacquer layer to an upper side of a printed medium. The first step of the method is forming a lacquer film. The next step is drying and/or hardening the lacquer film by at least one of heating and UV radiating the lacquer film. The next step is transferring the dried lacquer film to the freshly-printed upper side of the printed medium while simultaneously permanently adhering the lacquer film to the upper side.
With the objects of the invention in view, there is also provided an apparatus for applying a lacquer layer to an upper side of a printed medium. The apparatus includes a lacquer-transferring unit for producing a lacquer film and has a lacquer-transferring station and a radiator disposed downstream of the lacquer-transferring station. The lacquer-transferring station transfers the lacquer film to the upper side of the printed medium.
The crucial aspect of the present invention is thus that within a printing machine a lacquer film corresponding to a thin sheet of cellophane, in particular a nitro- or UV-lacquer film is produced from lacquer, this film is then dried or hardened under the action of heat and/or UV radiation, and subsequently it is transferred to the (fresh or still wet) printed upper side of a printed medium, becoming simultaneously glued to this upper side. In this way, it is possible without problems to provide a xe2x80x9cfaxc3xa7onxe2x80x9d type of lacquering, i.e. a lacquering only in regions covering part of the printed upper side of the printed medium. As a result of the drying or hardening of the lacquer, a film of lacquer is obtained that is equivalent to a cellophane film in that it does not xe2x80x9crunxe2x80x9d, i.e. blend with the still-wet ink on the printed medium.
Once the film of lacquer has dried or hardened, an adhesive, in particular UVC adhesive, can be applied to to form a film that is a composite of lacquer and adhesive. Subsequently, the composite film can be transferred, with the adhesive side down, onto the printed upper side of the printed medium.
Preferably, the adhesive is hardened, in particular by using infrared or ultrasoundxe2x80x94either immediately after application to the lacquer film or after the lacquer-adhesive composite film has been transferred to the upper side of the printed medium.
To form a glossy lacquer surface, lacquer is first applied to a transfer surface, in particular a transfer drum, that is highly polished, preferably has a ceramic coating. The transfer to the upper side of the printed medium is then done in such a way that the side of the lacquer film that is apposed to the highly polished, in particular ceramic surface, defines the upperside of the lacquered printed medium, i.e. the side that is viewed.
A ceramic-coated transfer surface has the advantage that once the lacquer film has hardened, it can be released therefrom with no problems, without impairing the glossy surface of the lacquer film.
In the case of a so-called faxc3xa7on lacquering, a lacquer-adhesive composite film is produced on only a specified region of the transfer surface, so that it can then be transferred or applied to the desired region of the printed upper side of the printed medium.
Experience has shown that the use of adhesive can be eliminated when the lacquer film is adjusted to a prespecified temperature, in particular about 80xc2x0-110xc2x0 C., at which it is hardened but nevertheless remains self-adhesive with respect to surfaces at lower temperature. In this situation it can be released from the highly polished transfer surface without difficulty and immediately transferred to the (fresh or still wet) printed upper side of the printed medium so as to become intimately joined thereto.
As an alternative to the above-mentioned embodiments of the method (lacquer-adhesive composite film or warming of the adhesive to a prespecified temperature), the dried or hardened lacquer film can be transferred to a printed upper side of the printed medium that has already been provided with adhesive. The adhesive can then be hardened after application to the film to printed upper side of the printed medium. Preferably, this hardening is brought about by the action of heat and/or UV radiation.
In accordance with a further object of the invention, a preferred apparatus for implementing the method includes a lacquer-transferring unit that is constructed for production of a lacquer film and includes a lacquer-transferring station, after which is disposed a station for hardening the lacquer, in particular in the form of a heating or UV-irradiation device; the lacquer film thus produced can then be transferred to the upper, i.e. printed side of the printed medium. The lacquer-transferring device includes a highly polished transfer surface, in particular a ceramic, stainless-steel, or chromium surface, for the reasons explained above.
In a preferred embodiment of the apparatus in accordance with the invention, the lacquer-transferring device includes a transfer drum, the surface of which is made of highly polished stainless steel, chromium, or non-ferrous materials, in particular ceramic.
In a preferred embodiment of the apparatus, the lacquer-transferring unit also includes an adhesive-transferring station disposed after the lacquer-transferring station. Between these two stations the radiation device is situated, e.g. a heat or UV radiator. As a result, a lacquer-adhesive composite film is formed that can be transferred to the printed upper side of the printed medium.
In an alternative embodiment of the apparatus, an adhesive-transferring station to transfer a film of adhesive to the upper side of the printed medium can be disposed ahead of the lacquer-transferring unit. In this case the lacquer-transferring device is used to apply the film of lacquer to the upper side of the printed medium after the latter has been provided with a film of adhesive. An adhesive-hardening device is preferably also disposed between the adhesive-transferring station and the lacquer-transferring device.
An adhesive-drying device is included in the lacquer-transferring unit, downstream of the adhesive-transferring station. Preferably, the adhesive-drying device is positioned after the transfer station in which the lacquer film or lacquer-adhesive composite film is applied by way of its adhesive side to the upper side of the printed medium.
It has proved especially advantageous to use as adhesive-drying device a UV radiator, an IR radiator or an ultrasound generator.
The transfer of the lacquer film or lacquer-adhesive composite film is preferably performed in a gap between the transfer surface and a counter-roller.
For xe2x80x9cfaxc3xa7onxe2x80x9d-type lacquering the lacquer and, where appropriate, the adhesive, are applied in a corresponding manner, e.g. with a high-pressure cylinder, only to specified regions of the transfer surface in the lacquer-transferring unit.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and apparatus for applying a layer of lacquer to the upper side of a printed medium, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.